I had the opportunity sneak away from work to the range this afternoon and run some various ammo through some different mags. Here were my results. Gun: Bushmaster A2. Mags: English GI, Orlite, USGI. Ammo: PMP, Silver Bear, 1989 MilSurplus SS109. Long story short, and this will probably not be news to non-newbies, PMP and SS109 ran though all mag types, new and old, without any problems. The Silver Bear would only feed in the USGI mags. The USGI mags, new and old, produced no jams with all ammo. So, I suppose my conclusion at this point is, either use USGI mags and don't worry about the ammo,or only use brass cased ammo so that most quality mags will feed properly. Actually, to be on the safe side, I am also sticking to USGI mags. Even the really ugly ones that only cost $10 work great.